Codeigniter. Implementing oAuth
I am not familiar with this library myself, but just had a look and it looks like you just want to download the library and copy all of the folders in the downloadable zip into your Codeigniter application directory. If you look in the controllers folder of the downloaded zip file, you'll see 2 controllers which show how the library is being used.
The two files are oauth.php and signin.php. They appear to show how you can login in a user via oAuth. Just carefully go through the files and you'll work it out.
I tried this extension a few days ago and i got i working. You need the edit the config-files, config/oauth_client.php, config/oauth_resource_server.php and maybe config/rest.php.
You also need the add at least one application to the database. One row in the applications-table is enough. Use the same client_id and client_secret as you used in the client config-file and it should work.